The statements in this section are intended to provide background information related to the present disclosure and do not constitute prior art.
The laryngeal adductor reflex (LAR) entails brief bilateral closure of the true vocal folds (VFs) in response to mechanical or chemical stimulation of the laryngeal mucosa. This defensive airway reflex provides protection from material inappropriately entering the lungs. It is therefore no surprise that LAR impairment correlates with pharyngeal dysphagia and aspiration, as well as other conditions, which are highly correlated with morbidity and mortality.
The clinical procedure for evaluating the LAR is air-pulse laryngopharyngeal sensory testing, performed as part of a flexible endoscopic evaluation of swallowing. This procedure entails transnasal passage of a flexible laryngoscope, typically without topical anesthesia, to deliver air pulses to the arytenoid mucosa and/or other mucosal targets at the entrance of the larynx (e.g., aryepiglottic folds), with left/right sides tested separately. An air-pulse device, such as the AP-4000; Vision Sciences, Pentax, and Medtronic, is used in this procedure to generate pulses of air between 50-millisecond to 1-second durations at incrementally increasing pressures, ranging from approximately 2 to 10 mm Hg. Air pulses are delivered through the endoscope working channel or side channel sheath, with the endoscope tip positioned 1 to 2 mm away from the arytenoid mucosa and other mucosal targets at the laryngeal entrance. This extremely short working distance limits visualization to only the ipsilateral arytenoid or other mucosal targets, which restricts quantification to a single metric: threshold air pressure that evokes ipsilateral medialization of the arytenoid or other mucosal targets, determined separately for each side. Requiring pressures >4 mm Hg to evoke a response or having an asymmetric or absent response is suggestive of sensory pathology, although it is not pathognomonic for any specific disease process.
LAR impairment has been identified in numerous conditions and pathologies, such as Parkinson's disease, cerebrovascular accident, chronic cough, adductor spasmodic dysphonia, and acid reflux disease, among others. In amyotrophic lateral sclerosis (ALS), 54% of cases have elevated sensory thresholds (>4 mm Hg), which suggests that LAR impairment can be a major contributing factor of aspiration pneumonia, a leading cause of death in this disease. LAR impairment has also been identified in healthy aging individuals, with progressive increases in pressure thresholds occurring each decade of life. This finding corresponds with increased incidence of silent aspiration in healthy older individuals, placing them at risk for aspiration pneumonia. Despite the negative outcomes associated with LAR impairment, effective treatments are lacking, likely due at least in part to limitations in the clinical procedures to evaluate the LAR and the limited scientific knowledge of underlying pathological mechanisms.
Some research has been done to improve the commercial AP-4000 system. However, these attempts/devices are regulated air pressure systems that manually trigger air pulses by opening a solenoid valve to release pressurized air from a reservoir. This pressurized air is delivered through a channeled endoscope into the throat of a patient to target the mucosa at the entrance of the larynx, which is innervated by the superior laryngeal nerve. Mechanical stimulation of this area evokes the laryngeal adductor reflex (LAR), identified as brief closure of the vocal folds to protect the airway. All of these devices permit measurement of a single metric: threshold pressure that evokes the LAR. Ranges for normal and abnormal pressure threshold responses have been defined using predicate air pulse devices. Abnormal threshold responses are indicative of laryngeal pathology but not pathognomonic for any specific disease process.